The applicants state that WITS is a seminal study of perinatal HIV infection. The overall objectives of WITS III will be to examine the mechanisms and co-factors of perinatal transmission, to examine the factors predicting disease progression and course of acute infection, and to examine the impact of pregnancy on HIV infection. The Chicago Consortium has been a member of the study group since the beginning of WITS I. It consists of study sites at University of Illinois at Chicago, Cook County Hospital, Northwestern University, and Children's Memorial Hospital. It has enrolled 309 HIV infected pregnant women and 237 of their infants. It will continue to enroll 50 HIV infected pregnant women annually. The Chicago consortium, according to the applicants, has provided scientific and managerial leadership to the national WITS agenda through participation of its members in leadership positions on committees and working groups, through the proposal and implementation of specific protocols, and the presentation and publication of results. The measures of quality of enrollment, retention, and data collection have demonstrated the high quality of the work. The application also proposes a scientific collaboration with an independently funded investigator, Dr. Alan Landay. The study will examine the immune function in pregnant HIV infected women. It will examine in greater depth the function changes that normally occur in pregnancy, the effect of HIV infection on these changes, the effect of the immune changes on perinatal transmission, and the effect on HIV disease progression. The applicants state that the proposed study closely follows the goals of WITS III and will add depth and texture to the study. The proposed plan will continue the work of the Chicago team in WITS III. The innovative characteristics, quality of work and efficiency of the group, according to the applicants, will enhance the overall scientific agenda of WITS III.